The Lexus RX450h Hybrid uses the gas/electric combo to drive the front wheels. The AWD version adds a small electric motor to drive the rear wheels. Not quite the same as the Model X but probably as close as you'll get out of the current production lineup.

My bud and I have been beating around the idea of doing a four motor brushless controller using one of these PPC embedded processors used for modern fuel controls. The ETPU could be used for very fast motor control while other on board hardware could be used to memory map gyros, magnetometers, accelerometers and the like. I remember F1 starting to play with electronic diffs and differential braking with good results. I can just imagine what four independent motors could do with very high speed updating of forward and reverse torque

Actually the Mercedes SLS Electric Drive has four engines, one engine on each wheel. But IMO also in the case of the Model X AWD (two engines) you could have torque vectoring, meaning to have instantaneously the torque available on each wheel (or the brakes of course) as wished by the ESC.
Maybe somebody knows more on this matter and how the AWD works for Tesla?

My Pisten Bully has two hydraulic engines for each side, with actuators. Power for the hydraulics comes initially from a Merc diesel. - I am going to bet that even Bonnie's loader could outrace it, but NOTHING can go up, or down, a steep mountainside with as much ease.

My Pisten Bully has two hydraulic engines for each side, with actuators. Power for the hydraulics comes initially from a Merc diesel. - I am going to bet that even Bonnie's loader could outrace it, but NOTHING can go up, or down, a steep mountainside with as much ease.

When covered with snow.

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But I could flatten that steep mountainside in a heartbeat. Just sayin'.